This invention relates generally to a caster having a central locking device for arresting its wheel.
Traditional central locking casters comprise a wheel mounted on a fork, the fork having a sleeve that houses a plunger or push rod, and a mushroom-shaped breaking member mounted on the bottom of the plunger or push rod that engages the perimeter of the wheel in order to lock it. Examples and variations of such casters are disclosed in U.S. Pat. No. 3,911,525 to Haussels; U.S. Pat. No. 4,414,702 to Neumann; and U.S. Pat. No. 5,774,936 to Vetter.
A disadvantage of several traditional central locking casters is their yokes often fail prematurely under heavy loads. For especially heavy loads (such as with bariatric beds), double wheel casters typically perform better under heavy loads and in circumstances where maneuverability is critical. For obvious reasons, traditional central locking mechanisms are not as suitable for double-wheeled casters as they are for single-wheeled casters.
Many alternative braking mechanisms have been designed for casters. U.S. Pat. No. 3,914,821 to Screen, for example, discloses a foot-operated brake linked to a brake shoe that engages an inner surface of the roller. Another patent to the same inventor, U.S. Pat. No. 4,747,180, discloses a braking system for a caster comprising a cam-activated brake rod able to extend all the way to the floor to prevent movement. U.S. Pat. No. 5,014,391 to Schulte discloses a brake lever bearing a sharp-toothed brake member that interacts with a brake rim. U.S. Pat. No. 4,550,808 to Folson discloses a caster having a foot-operated brake lever that acts against a link, which in turn acts against a brake shoe comprising two side arms or flanges that xe2x80x9cactually dig intoxe2x80x9d the inside surface of the outer cylindrical flange of the caster wheel. Darcor(copyright), based in Toronto, Canada, markets a caster wheel designed in particular for bariatric beds that utilizes a push rod that acts upon a spring-loaded brake arm bearing sharp teeth to mate against an inner surface of the roller wheel.
Many problems have been encountered with existing teeth-based brake designs. The teeth can break off prematurely, destroying the caster""s braking function. Moreover, the teeth prematurely wear out the braking surface of the wheel. Another problem encountered with one commercially popular brake-arm design is that the brake arm is loosely anchored in a manner that allows it to rock from side to side, instead of pivoting exclusively about a horizontal axis perpendicular to the direction of the wheel""s forward rolling movement. The biasing spring force is also poor. Therefore, when the caster wheel is jarred, as occurs when rolling a bed over a bump, the sharp teeth of the brake arm may grab the wheel even when the wheel is not engaged by the push rod, causing the caster to brake when it is not supposed to. Even worse, the brake arm may wedge into the wheel as it continues to turn, causing the caster to permanently lock up.
What is needed is an improved central braking mechanism for a high-load bearing caster.
The invention is directed to, but not limited by, one or more of the following non-exhaustive objects, separately or in combination:
to pvide a high-load, high-performance caster with a central-locking system suitable for bariatric beds, the caster having two wheels mounted on a axle of a sturdy yoke integrally formed with a semi-cylindrical cap or flange covering the top surface of the gap between the wheels;
to provide a twin-wheeled caster with a spring-loaded double-armed brake lever central locking mechanism;
to provide caster wheels comprised of an aluminum-core disc and an annular cylindrical flange covered with elastomeric material, an inside, elastomeric-covered concave surface of the annular flange serving as a brake drum for the wheel;
to provide a pivot pin to guide the spring-loaded double-armed brake lever so that it pivots exclusively about a horizontal axis perpendicular to the direction of the wheels"" forward rolling movement;
to provide a pivot block with an aperture for receiving the pivot pin for mounting the double-armed brake lever;
to provide two compression springs having sufficient spring force to bias the double-armed brake lever away from the wheel;
to provide recesses in the pivot block for anchoring an end of each of the compression springs, the opposite ends of the compression springs being disposed to provide a pushing force against a saddle portion of the double-armed brake lever in order to bias the brake arm away from the brake drum;
to provide an aperture extending vertically through the top and bottom of the pivot block in which to receive a flathead screw to mount the pivot block to the yoke;
to provide teeth on each arm of the brake lever to grab the elastomeric material on the inside surface of the corresponding wheel""s annular flange in order to inhibit wheel rotation;
to provide smoother, wider, and flatter teeth than typically used or taught in the caster brake art to minimize wear of the elastomeric material on the wheel""s annular flange;
to provide this caster for use on office furniture, computer furniture, and hospital beds, examples of the latter of which are disclosed in U.S. Pat. No. 6,115,860 to Vrzalik; U.S. Pat. No. 5,611,096 to Bartlett, et al.; and U.S. Pat. No. 4,638,519 to Hess; and PCT/US97/21285, filed Nov. 17, 1997, the details of all four of which are herein incorporated by reference; and
to provide this caster for use on bariatric products, including beds, chairs, wheelchairs, and walkers.